Field of the Invention
The present invention relates to an electrophotographic image forming apparatus.
Description of the Related Art
Conventionally, in the electrophotographic image forming method, a surface of an image bearing member is charged, the charged surface of the image bearing member is irradiated with light to form an electrostatic latent image, the electrostatic latent image is developed with a coloring toner to form a visible image, the toner image is transferred to a transfer sheet, and the transferred toner image is fixed with a heat roller. After the transfer process, an external additive, an untransferred toner, and a discharge product remaining on the surface of the image bearing member need to be removed by a cleaning unit prior to a next image forming process. The cleaning unit for removing, for example, the transfer residual toner, employs various methods, such as a method using a fur brush or a magnetic brush, and a method using an elastic cleaning blade. Since using of the cleaning blade which rubs the image bearing member to scrape the toner from the image bearing member is simple and inexpensive, it is generally used.
With the recent acceleration of operation speed of image forming apparatuses and enhancement of image quality, the shape of toner particles used by the image forming apparatus becomes more spherical. This causes difficulty in cleaning the toner by only the cleaning blade. Thus, a cleaning auxiliary unit for supporting removal of transfer residual toner is provided. For example, a fur brush that contacts the image bearing member is arranged in front of the cleaning blade, so that transfer residual toner before reaching the cleaning blade is removed by the fur brush. The pre-cleaning operation performed by the fur brush reduces a load of the cleaning blade and enhances cleanability. Such a technique is discussed in Japanese Patent Application Laid-Open No. 2009-300860, for example.
In Japanese Patent Application Laid-Open No. 2009-300860, a brush roller to which a bias can be applied is arranged on an upstream side of a cleaning blade to support a cleaning operation. Moreover, enhancement of cleanability is discussed. A bristle density of brush or a resistance value of brush is defined to increase a contact probability between the brush roller and toner, so that the cleanability is enhanced.
The fur brush has not only a function of cleaning a surface layer of a photoconductor, and also a function of grinding the surface layer of the photoconductor. In Japanese Patent Application Laid-Open No. 2009-300860, however, grinding of the surface layer of the photoconductor and an abrasion amount of the surface layer of the photoconductor are not precisely defined. The abrasion amount of the surface layer of the photoconductor varies depending on a hardness of the surface layer of the photoconductor and a bristle condition of the fur brush.
Recently, a configuration for increasing a hardness of a surface layer of a photoconductor is employed to prolong the lifetime of the photoconductor. If the surface layer of the photoconductor is hard, a grinding amount or an abrasion amount of the surface layer of the photoconductor tends to be reduced. Consequently, discharge products are accumulated. This degrades a surface property of the photoconductor, and thus the lifetime of the photoconductor cannot be sufficiently prolonged.